Phosphazene–chitosan based COF film with exceptional iodine capture and recyclability

Abstract

Radioactive iodine is a priority contaminant in nuclear-waste management because of its volatility, mobility, and toxicity, creating a need for sorbents that combine high capacity with stability, regenerability, and practical handling. Covalent organic frameworks (COFs) offer high surface area and tunable functionality for iodine capture, but many high-performing systems remain as powders that are difficult to deploy. Here, an imine-linked cyclotriphosphazene-based covalent organic framework (MA-COF; iodine uptake of 9.4 g g⁻¹ in powder form) is integrated with chitosan to fabricate flexible MA-COF@CS composite membranes. The imine-linked framework structure and permanent porosity of MA-COF are confirmed by complementary FT-IR spectroscopy, powder X-ray diffraction, nitrogen sorption analysis, and chemical stability tests. The optimized membrane (MA-COF:chitosan = 2:1, w/w) achieves an iodine vapor adsorption capacity of 10.50 ± 0.13 g g⁻¹ at 80 °C (n = 3) and removes 97.3 ± 0.5% of iodine from an I₂/cyclohexane solution (C₀ = 300 mg L⁻¹) at room temperature (n = 3). The membrane retains framework ordering after exposure to harsh solvents, remains stable up to ∼400 °C under N₂, and maintains adsorption performance during repeated adsorption–desorption cycles. Regeneration is rapid in ethanol, with 73.6% and 80.4% of iodine desorbed within 10 and 60 min, respectively. These results demonstrate a processable COF–biopolymer membrane sorbent that bridges high-capacity iodine capture with operational reusability and handling requirements relevant to nuclear-waste remediation.